iodide and salicylates all pass through the skin in quantities sufficient to 

 produce local deep effects if they are combined with suitable bases such as 

 the oils, wool-fat, and alcohol, and especially if they are aided by heat or 

 rubbing or both. Such bodies as ammonia, chloroform, camphor, and tur- 

 pentine, which by a local action after absorption lead to a dilatation of the 

 vessels of the skin, aid in the more rapid absorption of such other bodies 

 as can penetrate the skin, and this forms one reason for their inclusion in 

 ointments, liniments, plasters. If the student, with these ideas in mind, 

 will examine the pharmacopceial liniments and ointments he will gain a 

 good idea of how he may perscribe for local and reflex effects by way of the 

 skin. 



Lead Plaster is largely used for mechanical and supporting purposes, 

 but none of the other pharmacopoeial plasters save those of Cantharis and 

 possibly Belladonna are frequently employed. 



An antiseptic in the form of boracic acid 5%, salicylic acid l /^%, or 

 benzoic acid 1%, is frequently added to dusting powders consisting of 

 talc, starch, or zinc oxide, or to ointments containing some such inert pro- 

 tective powder, (e.g. Unguentum Zinci Oxidi). 



In many cases a purely superficial effect on the skin is desired. Anti- 

 septics must often be applied to the skin in order to kill pediculi or disease 

 germs which are lying upon it. For this purpose phenol in ^-2% watery 

 solution, mercuric chloride 1-500-2000, boracic acid in a saturated solution, 

 are amongst the common drugs used. If the skin be abraded, very much 

 weaker solutions of phenol or mercury must be applied, otherwise sufficient 

 antiseptic would be absorbed to produce a remote effect, or they may be 

 replaced by less readily absorbed antiseptics such as iodoform, ichthyol, 

 thymol, or re^orsin. In any such case, one of the above drugs may be applied 

 in the form of an ointment whose base is not readily absorbed by the skin. 



A very considerable insight into the character of preparations intended 

 for external use may be gained by the examination of the examples of 

 liniments and ointments and of the preparations of mercury. If the con- 

 stituents and bases of the following preparations of mercury are examined 

 it may be seen that the Emplastrum Hydrargyri, Emplastrum Ammoniaci 

 cum Hydrargyro, Unguentum Hydrargyri Oxidi Flavi, Unguentum Hyd- 

 rargyri Oxidi Rubri, Unguentum Hydrargyri Ammoniati, and the Lotio 

 Hydrargyri Flava vel Nigra would be relatively slowly absorbed; the Un- 

 guentum Hydrargyri Compositum, Unguentum Hydrargyri lodidi Rubri, 

 Unguentum Hydrargyri Oleatis, Unguentum Hydrargyri Subchloridi, 

 more readily; while the Unguentum Hydrargyri Nitratis and Linimentum 

 Hydrargyri will be still more readily taken up. The first group of these 

 would therefore be more generally used for purely external and local 

 purposes where they would act as antiseptics. The last group might readily 

 be used for remote and specific effects. 



From the inlets of the body covered with mucous membranes, drug- 

 stuffs are much more readily absorbed than from the skin. Drugs applied 

 to them can readily be made to exert a remote action. 



109 



